Operating systems and the applications that run on them have many tasks to perform which are sometimes difficult to achieve without having conflicts between one type of application and another. At the simplest level, an operating system is responsible for two basic aspects, whereby the system manages the hardware and software resources of the system. In a desktop computer, these resources include such components as the processor, memory, disk space, and so forth, whereas on a cell phone, the resources include the keypad, the screen, the address book, the phone dialer, the battery and the network connection, for example. The operating system should provide a stable, consistent way for applications to interact with computer hardware without having to be concerned with all the details of the respective hardware.
The first task of the operating system, managing hardware and software resources, is very important, as various programs and input methods compete for the attention of the central processing unit (CPU) and demand memory, storage and input/output (I/O) bandwidth for differing purposes. In this capacity, the operating system plays the role of the system manager, making sure that each application receives the necessary resources while properly interacting with all the other applications, as well as monitoring the limited capacity of the system to the greatest benefit possible of all the users and applications. This often requires balancing needs between competing applications.
The second task of the operating system, providing a consistent application interface, is especially important if there is to be more than one of a particular type of computer using the operating system, or if the hardware making up the computer is open to change. Thus, a consistent application program interface (API) allows a software developer to write an application on one computer and have a high level of confidence that it will run on another computer of the same type, even if the amount of memory or the quantity of storage is different on the two machines, for example. Even if a particular computer is unique, the operating system can ensure that applications continue to run when hardware upgrades and updates occur. This is by design since the operating system and not the application is charged with managing the hardware and the distribution of its resources.
Within the broad family of operating systems, there are generally four types, categorized based on the types of computers they control and the sort of applications they support. These categories can include:
Real-time operating system (RTOS)—Real-time operating systems are used to control machinery, scientific instruments and industrial control systems. An RTOS typically has very little user-interface capability, and generally no end-user utilities, since the system will be considered an embedded system when delivered for use. An important part of the RTOS is managing the resources of the computer so that a particular operation executes in about the same amount of time every time it occurs. For example, in a complex machine/controller scenario, having a part move more quickly because system resources are available may be just as catastrophic as having it not move at all due to the system being busy.
Another type of operating system includes single-user, single task. As the name implies, this operating system is designed to manage the computer so that one user can effectively do one thing at a time. The Palm OS for Palm handheld computers is but one example of a modem single-user, single-task operating system.
Similarly, a single-user, multi-tasking system may be provided. This is the type of operating system most people use on their desktop and laptop computers today. The most popular of these are Microsoft's Windows and Apple's MacOS platforms that are both examples of operating systems that allow a single user to have several programs in operation at the same time. For example, it's common for a user to be writing a note in a word processor while downloading a file from the Internet while printing the text of an e-mail message.
Multi-user is till yet another type of operating system. A multi-user operating system allows many different users to take advantage of the computer's resources simultaneously. The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn't affect the entire community of users. Some examples include Unix, VMS and mainframe operating systems, such as MVS.
With respect to single-user, multi-tasking systems, conflicts can exist for applications that were created under previous designs of the operating systems and in view of newer designs. Thus, these applications often follow the rules of the previous designs from an operational standpoint yet still need to operate with newer systems, applications, and contexts. In one example, current or legacy “File Systems” generally only support a single-item access API to create/modify/read file/directory data. However, newer, richer storage platforms may employ multi-item access rules and expose additional API sets which can be used to create/modify/read manipulate file/directory data as well. Given this requirement between older and newer applications running on the same system, there is a need to facilitate cooperation between such applications.
One area where differences exist between older and newer platform operations include synchronization and serialization processing. For example, if two threads were trying to create the same file name concurrently, one thread should have success creating the file and the other thread should fail—possibly generating an error message. Operating system components monitor such activities and arbitrate when conflicts exist. In previous platforms, such synchronization logic was provided in what is referred to as kernel mode which is also related to another operating system state referred to as user mode. For instance, to avoid having applications that constantly crash, newer operating systems were designed with at least two different operating modes referred to as kernel mode and user mode. Kernel mode refers to logic that controls how the machine operates with critical data structures, direct hardware (IN/OUT or memory mapped), direct memory, IRQ, DMA, and so forth. User mode is more of a virtual execution environment and executes applications designed for the machine but is generally prevented access to key hardware operations. Due to design differences with newer platform architectures, it is exceedingly difficult to implement reliable synchronization and serialization logic in kernel mode.